More than 6.5 million copies have been printed of the highly anticipated sequel to the 2003 mega hit, as book stores around the world brace themselves for an unprecedented stampede from hungry fans.

As well as being one of the largest first print runs in publishing history, an electronic version of the novel, which took Brown five years to write, will be released on the same day.

It is also already at the top of Amazon’s best seller list.

“The Lost Symbol” features the star of the series Robert Langdon, the Harvard University professor, returning to solve another, as yet disclosed, mystery.

Experts say the latest book, to be published in Britain by Random House, is the most sought after novel since the last Harry Potter book.

Despite savage reviews, with critics including Salman Rushdie saying the books were an example of appalling writing, the series has became a worldwide phenomenon, with more than 81m copies in print.

The film, which starred Tom Hanks as Langdon, got even worse reviews but stunned critics by taking almost £500 million at the box office.

Extraordinary measures have been taken to keep the content’s under wraps, with the only detail the publishers have disclosed is that it takes place over a 12-hour period in Washington.

Guards have been posted at book warehouses across the globe, anyone who has come into contact with the book has had to sign a non-disclosure agreement and the reclusive author has not done the usual pre-launch publicity tour, bar one interview with the popular Today programme in the US...